The Sequel combines a low profile shape with high end technology, creating a helmet that’s perfect for all-mountain adventures. The Hybrid shell construction is both lightweight and durable, while the BOA fit system allows for simple adjustment at the twist of a dial. Airflow can be controlled by sliding the switch on the top which opens/closes the vents.SmallMediumLarge51-55cm55-59cm59-63cmVenting: ActiveSizing System: AdjustableWeight: 520gConstruction: HybridSafety standard: eN 1077 Class B, ASTM F 2040